In the climatic battle scene in Rogue One: A Star Wars Story, basically everyone has a gun. The rebels dodging enemy blaster beams along the sand. The stormtroopers emerging from the water in their shiny white armour. The long-legged armoured walkers knocking down palm trees.

There isn't a single lightsabre to be found anywhere. Director Gareth Edwards has explained his weapon choices by saying that the events take place before the understanding of the Force in the story's universe.

But the omnipresent guns in the latest Star Wars movie also reflect a trend in Hollywood over the past 30 years toward increasing gun violence in superhero/fantasy/comic book-type action flicks aimed at children and teens - a shift that has created confusion about what differentiates a PG-13 movie such as Rogue One from an R-rated film. Think characters like Batman, Avengers, X-Men and Transformers.

In fact, according to a new analysis, the amount of gun violence in the 30 top-grossing PG-13 movies now exceeds the gun violence in the top R-rated flicks. And it is continuing to rise.

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The study, published yesterday in the journal Pediatrics, is an update to research that came out in 2013 and made headlines for its finding that prevalence of gun violence in top PG-13 movies had more than tripled since the rating was introduced in the mid-1980s.

The new analysis, says study author Dan Romer, research director of the Annenberg Public Policy Center of the University of Pennsylvania, suggests that "Hollywood continues to rely on gun violence as a prominent feature in its highly popular PG-13 action-oriented films".

Romer's research is important because, while the link between watching violence on the big screen (or on TV or in video games for that matter) and real-world violence is not well understood, there is evidence that such scenes may contribute more generally to aggressive behaviour and desensitisation to violence.

Until we know more, Romer and his co-authors write, paediatricians "should consider advising parents to be cautious about exposing their children to the gun violence in PG-13 movies".

The methodology used in both studies is similar and involves splicing the films into five-minute segments and noting whether a character fired a gun and hit another character during that time.

Multiple instances of gun violence were counted only once if they happened within the same five-minute segment. Researchers noted that in G.I. Joe: Retaliation, for example, there were 22 five-minute segments for a total of 1 hour, 50 minutes, and gun violence occurred in nine of the 22 segments - equalling roughly 40 per cent of the movie.

The original study involved looking at 945 top-grossing releases from 1950 to 2012; the new one covers films out from 2013 to 2015. The data clearly show that the amount of violence per hour of PG-13 movies continues to increase as compared to their R-rated counterparts.

The researchers attributed the phenomenon to the popularity of action movies for children and teens that contain a lot of what they call "bloodless violence" by comic book figures and expressed concern about the films' "erasure of the consequences" such as blood and suffering by more realistic characters.

Chris Ortman, a spokesman for the Motion Picture Association of America, said that the voluntary, 50-year-old ratings system, the Classification and Rating Administration, has changed over time to reflect the changes in "American parents' sensitivities".

"The purpose of Cara is ... to reflect the current values of the majority of American parents, and he pointed out that the ratings are assigned by a team of raters who themselves are parents."